Duplex transmission scheme

1. A method of multiplexing signals transmitted by a number of terminals onto a communications link; the bandwidth of the terminals exceeding the capacity of the link; the method comprising the steps of: i) monitoring the link for the occurrence of simultaneous transmission of signals over the link by two or more terminals; ii) assigning portions of the link capacity to the transmitting terminals; the sum of said portions being equal to or less than the capacity of the link; iii) varying an encoding rate of said signals transmitted by said terminals; and iv) varying a form of encoding, wherein said signals are digitally encoded; said bandwidth being varied by varying the rate of encoding; and wherein said signals are voice band signals and said encoding may be one of Adaptive Differential Pulse Code Modulation (ADPCM), Linear Predictive Coding (LPC), Adaptive Predictive Coding (APC), Multiple Excitation Linear Predictive Coding (MPC-LPC); whereby the bandwidth of the transmitted signals corresponds to the portions assigned to the terminals.

2. A method according to claim 1 wherein the link is a time division duplex link.

3. A method according to claim 1 wherein the link is a time division duplex link and said signals are encoded using a variable bit rate encoding scheme and wherein a 32 Kbits.sup.-1 capacity is allocated to a terminal when only one terminal is transmitting and wherein a 16 Kbits.sup.-1 capacity is allocated to both terminals when both are transmitting.

4. A system for the communication of signals in real time by a number of terminals over a channel; said system being adapted to vary the bandwidth of at least one signal such that the number of signals multiplexed onto said channel can be dynamically varied; wherein said signals are digitally encoded; wherein the channel is monitored for the occurrence of simultaneous transmission of signals over the channel by two or more sources; wherein portions of the channel capacity are assigned to the transmitting terminals with the sum of said portions being equal to or less than the capacity of the channel; said bandwidth being varied by varying an encoding rate of said signals; and wherein said signals are voice band signals and said encoding may be one of Adaptive Differential Pulse Code Modulation (ADPCM), Linear Predictive Coding (LPC), Adaptive Predictive Coding (APC), Multiple Excitation Linear Predictive Coding (MPC-LPC), a form of encoding said signals being varied such that the bandwidth of the transmitted signals corresponds to the portions assigned to the terminals.

5. A system as claimed in claim 4 wherein said channel is adapted for bi-directional communication.

6. A system as claimed in claim 4; wherein said channel is adapted for bi-directional communication; and wherein said channel is a Time Division Duplex channel.